Springs

From The Infiniti G37 Information Resource

This article is part of our special collection:

Suspension

This article is part of our special collection:

Parts

Aftermarket springs can improve performance, feel, and looks of your Infiniti G37. The stock suspension is designed to accommodate a wide range of drivers but you should tune the suspension to fit your personal taste. A lower car will have a lower center of gravity resulting in less body roll through corners.

Stiffer springs can help plant the car better, but choosing springs that are too stiff will result in undesirable feel and handling. If excessive stiffness is wanted, shock absorbers should be changed along with springs.

It is impossible to recommend the best spring for any application without defining which shock absorber is used. The 10kg/mm spring in most Japanese coilover kits are perfectly suited for the shocks they come with, but coupled with the OEM shocks (that were a 4.9kg spring) the ride and handling would be woeful.

Available Springs

Eibach Pro Kit Apprx Price: $249 Part #: 6388.140 F Drop: ??mm (??in) R Drop: ??mm (??in) F Stiffness: ? R Stiffness: ? Manufacturer: Eibach

Eibach Sportline Kit Apprx Price: $249 Part #: 4.8863 F Drop: ??mm (??in) R Drop: ??mm (??in) F Stiffness: ? R Stiffness: ? Manufacturer: Eibach

Spring Types

There are two types of spring designs: linear and progressive. This refers to their rates as the spring is compressed.

Linear springs have the same spring rate from the initial compression all the way to full compression. If a linear spring is rated at 6.2kg/mm (and lets say its range of movement is 50mm) then it takes 6.2kg to compress the spring from 0mm-1mm and 6.2kg to move it from 49mm-50mm.

A progressive spring will have a softer rate for its first few mm of travel, which then increases as you increase the load on it. Lets say we have a progressive rate spring with the same range of movement as above. While it may only take 4.4kg to move it from 0mm-1mm, it may need 7.1kg to move it from 49mm-50mm.

A progressive rate spring is clearly a compromise between softness for ride and firmness for handling. As such, it is more suited for the street. The softer initial rate gives it better compliance, especially over a low amplitude bump. But once you start loading up the suspension the firmer it becomes, so your flat-out cornering is improved.

A linear rate spring would be a better choice for the track, where you do not need to compromise handling for anything. Consistency in the spring rate gives you a better feel, since the car's weight shift isn't as variable. Since your springs are at maximum stifness, initial response is quicker as the car won't want to lean onto its outside suspension as much before the spring resists the movement and the car starts to turn.

From Car Bibles Web Site

Source: http://www.carbibles.com/suspension_bible.html
These come in three types. They are coil springs, torsion bars and leaf springs. Coil springs are what most people are familiar with, and are actually coiled torsion bars. Leaf springs are what you would find on most American cars up to about 1985 and almost all heavy duty vehicles. They look like layers of metal connected to the axle. The layers are called leaves, hence leaf-spring. The torsion bar on its own is a bizarre little contraption which gives coiled-spring-like performance based on the twisting properties of a steel bar. It's used in the suspension of VW Beetles and Karmann Ghias, air-cooled Porsches (356 and 911 until 1989 when they went to springs), and the rear suspension of Peugeot 205s amongst other cars. Instead of having a coiled spring, the axle is attached to one end of a steel shaft. The other end is slotted into a tube and held there by splines. As the suspension moves, it twists the shaft along it's length, which in turn resist. Now image that same shaft but instead of being straight, it's coiled up. As you press on the top of the coil, you're actually inducing a twisting in the shaft, all the way down the coil. I know it's hard to visualise, but believe me, that's what is happening. There's a whole section further down the page specifically on torsion bars and progressive springs.

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